First point: there is absolutely no reason to ask a politician about whether he or she would accept a VP invitation. None. Not even in the days leading up to the selection, and certainly not months in advance. It's simple: almost anyone offered the job would take it, but almost no one will say so in advance. So just don't ask.
Second point: polling people about how a VP pick would affect their vote choice is a total waste of time. Voters don't know what will affect their vote choice, and even if they are familiar with the politician in the question they can't predict how they would feel about that pol after the selection, and the convention speeches, and the rest of it. Nothing wrong with getting favorable/unfavorable ratings of various politicians, but that's about the best you can do now, and it's not much -- especially since non-disastrous VP picks usually make very little difference, anyway.
If people want to speculate about who the pick will be...well, idle chatter is part of the game. But c'mon, reporters: you have limited time to question politicians and limited resources to ask polling questions; might as well save them for something that's at least not a complete waste over everyone's time.